The present invention relates to a square mixed-cut gemstone having cut corners.
Gemstones, especially precious gemstones such as diamonds, emeralds, sapphires and rubies, have various characteristics that distinguish them from other gemstones. One characteristic is brilliance, which can be further categorized into external and internal. External brilliance, also referred to as luster, generally refers to the amount of light that impinges on the top of the stone and reflects back, rather than refracted inward. Internal brilliance is determined by the light rays that enter the top or crown (and table if the gem has one), and reflected off the base or pavilion facets and back out through the top or crown as undispersed light.
Another characteristic of a gemstone is dispersion, also known as fire, which is a measure of how much the white light is broken up into the spectral colors. A ray of white light striking a prism will be split up into special component colors of red, orange, yellow, green, blue, indigo and violet. Dispersion is maximized when a ray of light is reflected totally from base facets and strikes the ground facets at the greatest possible angle. Dispersion is observed when a gemstone moves relative to an observer.
Another characteristic of a gemstone is scintillation, which is an indication of the different light patterns obtained when the stone is moved under light. Expressed in another way, scintillation is the quantity of flashes observed from the gemstone when at least one of the gemstone, light source or observer moves.
Generally, gemstone cutters try to achieve a good combination of brilliance, dispersion and scintillation.
Gemstones may also be classified into different types of cuts. One cut is known as a step cut or emerald cut and is generally considered an elegant and classic cut. However, this cut does not generally achieve the most dispersion.
Another cut is known as a brilliant cut, which in one form is a round brilliant. This cut has many facets and achieves a good balance of brilliance and dispersion.
Yet another cut is a so-called hybrid or mixed-cut, which attempts to achieve the elegant and classic look of a step cut, while also attempting to achieve good dispersion as in a brilliant cut.
The present invention is directed to a mixed-cut gemstone, and includes attributes of both the step cut and brilliant cut types.
It is an object of the present invention to provide a mixed-cut gemstone having more dispersion than a step cut or emerald cut gemstone.
It is an object of the present invention to provide a mixed-cut gemstone having a substantially square shaped crown which is elegant and classic.
It is an object of the present invention to provide a mixed-cut gemstone having a brilliant cut pavilion which provides good dispersion.
It is an object of the present invention to provide a mixed-cut gemstone having the combination of the elegance and classic appeal of a step cut or emerald cut, with the good dispersion of a brilliant cut.
It is an object of the present invention to provide a mixed-cut gemstone having a substantially square shaped crown and having cut corners.
It is an object of the present invention to provide a mixed-cut gemstone which provides a good balance of very good brilliance, dispersion and scintillation.
It is an object of the present invention to provide a mixed-cut gemstone which provides good brilliance, dispersion and scintillation without a large number of facets on the pavilion.
It is an object of the present invention to provide a mixed-cut gemstone having substantially quadrature symmetry.
It is an object of the present invention to provide a mixed-cut gemstone having a table with a table percentage providing a good balance of brilliance, dispersion and scintillation.
It is an object of the present invention to provide a mixed-cut gemstone having essentially one culet, centrally located at the base of the pavilion, which is a point, line or a planar facet.
It is an object of the present invention to provide a mixed-cut gemstone having a crown and pavilion with matching side and corner portions.
It is an object of the present invention to provide a mixed-cut gemstone having a crown and pavilion with symmetrical side and corner portions.
It is an object of the present invention to provide a mixed-cut gemstone having a pavilion portion with rib lines extending substantially continuously from the girdle to the culet.
It is an object of the present invention to provide a mixed-cut gemstone having a table with a table size that is not too small as to lose brilliance, yet not too large as to lose dispersion.
It is an object of the present invention to provide a mixed-cut gemstone having a crown height which is not too shallow.
It is an object of the present invention to provide a mixed-cut gemstone having a stepped crown having a relatively small number of steps so as to not provide too much dispersion.
According to one aspect of the invention, a cut cornered mixed-cut gemstone is provided, comprising a girdle, a crown above said girdle and a pavilion below said girdle. The crown has a width and length formed by two pairs of opposing crown sides and four crown corners. The crown also comprises at least two steps, including a first step from the girdle to a crown break, and a second step from the crown break to a table break. The crown also has a substantially flat table. The pavilion comprises a substantially centrally located culet at the bottom of the pavilion, and also comprises two pairs of opposing pavilion sides and four pavilion corners defined by eight rib lines extending from the girdle to the culet. Each pavilion side and pavilion corner comprises four facets each having a facet corner intersecting at a facet intersection point. The four facets include a lower girdle star facet having one edge along the girdle, two lower girdle facets adjacent said lower girdle star facet and each having a side along an adjacent rib line, and a lower bezel facet adjacent said two lower girdle facets, with the lower bezel facet having two sides along adjacent rib lines.
According to another aspect of the invention, a cut cornered mixed-cut gemstone is provided, comprising a girdle having a length and width and being in a girdle plane, a crown above said girdle and a pavilion below said girdle. The crown has a width and length formed by two pairs of opposing crown sides and four crown corners. The crown also comprises two steps, including a first step from the girdle to a crown break having an angle of about 41-44 degrees relative to the girdle plane, and a second step from the crown break to a table break having angle of about 36-39 degrees to the girdle plane. The length of the longest crown side along the girdle is about three times the length of a crown corner along the girdle, and the length of the crown along its longest crown side is about 100 to 103% of its width along the shortest crown side. The crown also has a substantially flat table. The table has a size defined by its width, and is about 52-58% of the width of the crown at the girdle. The crown has a total of 17 facets. The pavilion comprises a substantially centrally located culet at the bottom of the pavilion, and also comprises two pairs of opposing pavilion sides and four pavilion corners defined by eight rib lines extending from the girdle to the culet. Each pavilion side and pavilion corner comprises four facets each having a facet corner intersecting at a facet intersection point. The four facets including a lower girdle star facet having one edge along the girdle, two lower girdle facets adjacent said lower girdle star facet and each having a side along an adjacent rib line, and a lower bezel facet adjacent said two lower girdle facets, with the lower bezel facet having two sides along adjacent rib lines. The pavilion has a pavilion length defined by a first pair of two opposed pavilion sides, and a pavilion width defined by a second pair of two opposed pavilion sides adjacent said first pair of opposed pavilion sides, said pavilion length and pavilion width being further defined by respective dimensions along the length and width of the girdle, and wherein the pavilion length is perferably between about 100 and 103% of the pavilion width. The pavilion has a total of 32 facets, exclusive of any culet facet. The gemstone has a total depth of about 65-71% of the width of the girdle.
Other objects and advantages of the present invention will become more apparent from the detailed description of the preferred embodiment, appended claims and attached drawings.